P51 wing loading

[RTHolmes]

interesting stuff Widewing, although I still wonder about how much the report's definition of "turning characteristics" releates directly to minimum flat turn radius.

overall I'm not surprised that the 51 isnt a great turner relative to similar aircraft because the wing is optimised for low drag rather than lift. am I right in thinking that loaded 51s climbed to alt with 1 notch of flaps?

the A20 is an interesting example, the wing was designed to lug a fully loaded (26,000lb) bird at a reasonable climbrate for the operations it would be used for, but not at 400mph, ie optimised for lift with a drag penalty. lose 7,000lb of ords and fuel and that lift and the power/weight ratio translates to a very tight turning circle.

[Widewing]

I'm not saying that the A-20 is incorrect.

The A-20G without bombs and 25% fuel weighs in at 18,738 lb. Its wing area is 465 sq/ft. This produces a wing loading of 40.3 lb per sq/ft.

P-51B, no ammo, 25% fuel weighs in at 8,213 lb. Its wing area is 235 sq/ft. This produces a wing loading of 34.9 lb per sq/ft.

P-40E, 75% fuel and drop tank weighs in at 8,430 lb. Its wing area is 236 sq/ft. This produces a wing loading of 35.7 lb per sq/ft.

Fw 190A-5, 25 fuel, 4 cannon weighs in at 8,158 lb. Its wing area is 197 sq/ft. This produces a wing loading of 41.4 lb per sq/ft.

My testing at the weights above (rounded to nearest foot measurement):
Turn radius, clean...

A-20G: 722 ft
P-51B: 770 ft
P-40E: 744 ft
190A-5: 787 ft (Mosq's data)


Turn radius, full flaps...

A-20G: 586 ft
P-51B: 601 ft
P-40E: 566 ft
190A-5: 584 ft (Mosq's data)

Clearly, there is something different about the P-51s... What I would like to know is: What is it?


My regards,

Widewing

[BnZs]

WTF is up with the Fw-190s?

The A-20 and P-51B experienced a 19% and 22% reduction in turn radius respectively comparing clean configuration to full flaps.

The 190A5 got a 24% reduction in turn radius. The thing that sticks out here is that it has Split-flaps, not designed for aiding maneuvering and not efficient for that purpose from a lift/drag ratio standpoint. Yet it gets as much turn radius benefit as the P-47s get from their maneuvering flaps and almost as much as a P-38J gets (26%) from full deployment of Fowler flaps!

[Badboy]

Guys

I'd just like to clarify a couple of points.

Firstly, wing loading is not a useful comparison in the context of this thread. It is only useful when you are discussing aircraft that have wings with similar lift coefficients. Generally, comparing fighters using wing loading values alone can be misleading, comparing bombers with fighters using wing loading is more so.

Secondly, bombers that have wings that can reach higher coefficients of lift, because they have been designed to carry heavy loads, often compare favourably with fighters if you do calculations on their turning ability when they are light. This has been a noticeable feature of almost every flight sim' that allows the players to fly bombers. Does that mean the fighters involved are wrong? Nope. If you look at the A20 in the file containing Mosq's data posted earlier in this thread you will notice that the A20 has a smaller sustained turn radius than the TA152, the P38L and P38J with heavy ammo, the P-51B, P-51D, the P47N with heavy ammo, the FW-190D9, FW-190A8 and FW-190F8. Does that mean there is something wrong with all of those fighters? Nope. I'd be surprised if anyone who flies any of those fighters as their main ride, would complain that they have any difficulty dispatching A20's in the MA. That's because very little of the air combat in the MA takes place under the sustained turning conditions illustrated by that data.

Lastly, I would like to point out as someone who is totally neutral on this issue, that none of the arguments or data presented so far in this thread lends any credibility to the contention that there is anything wrong with the P-51.

Badboy

[iTunes]

Guys

I'd just like to clarify a couple of points.

Firstly, wing loading is not a useful comparison in the context of this thread. It is only useful when you are discussing aircraft that have wings with similar lift coefficients. Generally, comparing fighters using wing loading values alone can be misleading, comparing bombers with fighters using wing loading is more so.

Secondly, bombers that have wings that can reach higher coefficients of lift, because they have been designed to carry heavy loads, often compare favourably with fighters if you do calculations on their turning ability when they are light. This has been a noticeable feature of almost every flight sim' that allows the players to fly bombers. Does that mean the fighters involved are wrong? Nope. If you look at the A20 in the file containing Mosq's data posted earlier in this thread you will notice that the A20 has a smaller sustained turn radius than the TA152, the P38L and P38J with heavy ammo, the P-51B, P-51D, the P47N with heavy ammo, the FW-190D9, FW-190A8 and FW-190F8. Does that mean there is something wrong with all of those fighters? Nope. I'd be surprised if anyone who flies any of those fighters as their main ride, would complain that they have any difficulty dispatching A20's in the MA. That's because very little of the air combat in the MA takes place under the sustained turning conditions illustrated by that data.

Lastly, I would like to point out as someone who is totally neutral on this issue, that none of the arguments or data presented so far in this thread lends any credibility to the contention that there is anything wrong with the P-51.

Badboy

+1 here, I'd also add that at say 20-25k doing combat speed in a pony, there wouldn't be a whole lot that could out turn you.

[Widewing]

Guys

I'd just like to clarify a couple of points.

Firstly, wing loading is not a useful comparison in the context of this thread. It is only useful when you are discussing aircraft that have wings with similar lift coefficients. Generally, comparing fighters using wing loading values alone can be misleading, comparing bombers with fighters using wing loading is more so.

Absolutely, CLmax is equally important with wing loading. Neither can define turn radius alone. However, the P-51's CLmax was not so low as to create the issue we see in the game.

NACA Report 829 states and clearly demonstrates that the P-51B, due to the extremely smooth and clean design of the wing, has a slightly higher Coefficient of Lift than the F4U-1A. This is when both wings are in "service condition". Moreover, the P-51B hits its max CL at a greater angle of attack than the Corsair. Why did the Corsair out-turn the P-51B in Navy comparison testing? Lower wing loading and the fact that the F4U had its wings taped (sealed), without which, its CLmax drops substantially due to intra-surface leakage.

The P-51B has a CLmax virtually identical to the P-47D, and a lower wing loading.... In the real world, the P-51B could handily out-turn a P-47D. This makes sense as turn radius is basically determined by the weight load carried by the wing divided by the wing's efficiency at lifting the load. In the game (clean condition), the P-47D-11 turns smaller circles than the P-51B, with the P-47D-40 nipping at the Mustang's heels. If you take the lesser ammo load in the Jug (which was what was usually loaded for combat in the 8th AF), it matches the P-51B. 

NACA 829 included CLmax testing of three aircraft with landing flaps fully extended... As expected, higher CLmax, occurring at much lower angles of attack.

The conclusions of NACA829 are interesting:




My regards,

Widewing

[Badboy]

Guys

The problem with discussions of this type is that there is often a great deal of misunderstanding about exactly what it is that is actually being compared. For example, because aircraft A has a higher lift coefficient and lower wing loading than aircraft B it is automatically assumed that aircraft A will be superior in turning, but that simply isn't always the case. Lift coefficient and wing loading even when taken together are not enough to make valid predictions about the outcome of a turning engagement.

I hear you asking… Am I really saying that an aircraft with a higher maximum lift coefficient and lower wing loading can be out turned by one with a lower maximum lift coefficient and higher wing loading? Absolutely, that's exactly what I'm saying. But it is important to be very clear about what we mean by “out turn”, just quoting turn radius and turn rate values is meaningless, we need to be sure if we are talking sustained or instantaneous turn values.   

The problem is that when people on these boards quote lift coefficients and wing loadings, and then compare them with turn radius and turn rate values, they are often using the turn rate and turn radius as determined in sustained turn tests. That data is important and useful to help predict the outcome of an engagement, and is readily available. The catch is that in a sustained turn, the performance depends very heavily on factors that are often ignored in the discussion. What factors? Well, in a sustained turn a lot depends on the ability of the engine and prop to pull the aircraft around the turn, so a large number of factors associated with the engine and propeller come into play.

So, if you are comparing lift coefficient and wing loading data for aircraft with different engine and prop configurations, the results may well be counter intuitive because the sustained turn rate may well be influenced more by differences in the thrust producing capability of the aircraft than by differences in lift and weight. As an example, I just ran the calculations for the case of the F4U1 and P-51B from the report cited earlier in this thread and the results show that even with a higher wing loading, and lower maximum lift coefficient the F4U1 can still achieve the higher sustained turn rate.

I think that result would surprise some people, and so I think it helps to illustrate the danger in trying to draw conclusions based on performance ratios, and unfortunately, there really aren't any reliable short cuts to this sort of thing.

What does all that mean? It all adds up to the conclusion that, as yet, we haven’t really seen a compelling argument regarding any particular comparison.

Hope that helps.

Badboy

[SgtPappy]

When WW states that the reasons as to why the F4U-1 'outturns' the P-51B in the Navy test, it is stated that there is experimental error involved. Perhaps even without the sealed wings, perhaps the F4U would still turn 'better' but not as much so. We don't know.

Additionally, I'm sure someone has thrust numbers here somewhere. I don't know off hand myself, but I believe the F4U-1 (P&W R-2800; no water injection/old propeller) produces slightly more thrust than a P-51B (V-1650-3/Hamilton Standard w/rubber slips). But a lot relies on the drag of the plane as well. I mean, what good is all this thrust if the drag penalty is really high? Hence, the lower thrust/lower drag P-51B and higher thrust/higher drag F4U-1 accelerate similarly.

That was just a simple deduction based on absolutely nothing but it I hope it makes you think. The P-51B - as discussed in previous other threads on the exact same topic - has one of the absolute lowest overall drag coefficients of any WWII fighter. 

[dtango]

SgtPappy:

Badboy know's what he's talking about and is absolutely spot on in what he states .

Tango, XO
412th FS Braunco Mustangs

[dtango]

SgtPappy:

I should elaborate just a little since I posted my earlier response on the way out of the office .

Thrust and drag are not single point values.  In the case of thrust it varies with airspeed and besides engine BHP is also highly dependent on propeller efficiency which is a function of propeller aerodynamics.  Drag is obviously not a single point value either and varies with both speed, configuration, and lift.

The point is that often folks tend to over-generalize the aerodynamics which leads to picking on your favorite aerodynamic variable and trying to make some conclusion from it but don't realize it's incorrect.  Your thrust and drag assumptions of the F4U and the P-51 are is an example of this kind of over generalization.  It is aero-"DYNAMICS" afterall, meaning that the forces involved are complex and change so that what you find in one flight condition can be dramatically different in a different condition for the same airplane.

Tango, XO
412th FS Braunco Mustangs 

[BnZs]

The P-51s turning abilities or lack thereof relative to certain other aircraft does not match what virtually all the test and combat reports we have say, and as you have admitted seem rather odd in light of the physical traits of the P-51 vs. other aircraft. Widewing in his many posts on this matter has dug up as much empirical evidence as you are likely to get on "real world" testing.  With this mass of evidence in mind, what proof can naysayers present that the P-51 modeling is NOT wrong, and what explanation can be given for so many persons making such a grave error about the P-51 relative maneuvering qualities, especially since such an error was liable to be fatal to combat pilots?

[Boozeman]

Well, we got some test data about the turn radius, but what about the corresponding turn rate? When the turn radii are similar, then the turn rate will make the difference. 

[SgtPappy]

dTango, Badboy,

I hope it didn't look like i was critisizing everything. I was simply stating a rebuttle. I am here to learn after all, and hope to study aerodynamics myself in about 7 months time.

But what I can't understand are the conflicts between the real-world data vs. AHII data and the real-world data vs. itself.

As an example, we have all seen the numerous tests stating that the Mustang III handily has a better sustained turn than the Tempest V, that is, turns inside the Tempest V. We don't see that in game. It is also found that though the P-47D's have lighter controls, that they have a slower turn rate vs. the P-51B.

But then again, the data is confusing. AFDU stating that the 109G6 cannot turn inside a P-47 or even Fw190.

[Stoney]

But what I can't understand are the conflicts between the real-world data vs. AHII data and the real-world data vs. itself.

How many history books have errors in them?  Most of the time, its due to poor research, bias, or questionable reference material.  The 1940's were some of the best and worst times for aerodynamic research.  Many groundbreaking discoveries were made, but some of the worst aviation myths were also created.  Simple scientific method was sometimes completely ignored, even by NACA, the USAAF, the RAF, etc.  Objectivity was often questionable, even if the bias was inadvertent.  Additionally, different sources of information from the period directly contradict each other.  Who or what do you believe in these situations? 

Its ironic that this discussion revolves around one of the most famous and thoroughly documented aircraft in history.  Coincidence?

[dtango]

dTango, Badboy,
But what I can't understand are the conflicts between the real-world data vs. AHII data and the real-world data vs. itself.

The problem is we have no earthly idea what the supposed "data" even means.  The oft referenced report is this AFDU doc with something about comparison of turning circles.  Some people seem to think they know what kind of turn data it is - e.g. it must be the best sustained radius.  I have no clue as to how they could even make that conclusion.

For all practical purposes it's pretty much crap for us.  There's not even any hint of how the turns were performed and under what plethora of conditions.  Nothing.  On top of that there isn't even any turn radii data at all.  Zip.  None.  Nothing that we can even use to know exactly what it was we are comparing.  There's no data point to even begin to try and understand.

I have another AFDU in 1945 report comparing the Mustang III with the Spit IX, Spit XIV, Tempest V, Fw-190, and 109G.  Guess what it says about the turning circle of the P-51 in relationship with the Fw190 and 109G?  The P-51 is slightly better than the Fw190 while it's tremendously better than the 109G.  So why is the Fw190 all of the sudden better than the 109G while in the quoted AFDU report here in the thread the diagram show the Fw190 and 109G the same?  Hmm.  Go figure.  Unfortunately my AFDU report is just about as useless because it doesn't give us any relevant info to understand what the heck they are really comparing.

Interestingly enough at least my AFDU report gives a really vague statement about possible turning conditions in the section comparing the Fw190 turning circle with the Mustang.  It states...

Turning Circle
...The Mustang is always slightly better.  When evading an enemy aircraft with a steep turn, a pilot will always out-turn the attacking aircraft initially because of the difference in speeds.

What the heck is that supposed to mean?  Beats the crap out of me, but it sure doesn't sound like a comparison of best sustained turn radii of the aircraft.  I could speculate but it's pretty pointless because we don't have any real reference point to understand what type of turning they are really comparing.

I and others have stated it already in multiple different ways.  The bottom line is the AFDU "turning circle" drawing is useless as any real form of comparison.

Tango, XO
412th FS Braunco Mustangs